One approach to achieving nanometer (nm)-scale feature sizes in semiconductor devices is to use shorter wavelengths of light when exposing photoresist layers. However, the difficulty in finding materials that are transparent below 193 nm exposure wavelength has led to the immersion lithography process to increase the numerical aperture of the lens by use of a liquid to focus more light into the film. Immersion lithography employs a relatively high refractive index fluid between the last surface of an imaging device and the first surface on the substrate being treated, for example, a semiconductor wafer.
In immersion lithography, direct contact between the immersion fluid and photoresist layer can result in leaching of components of the photoresist into the immersion fluid. This leaching can cause contamination of the optical lens and bring about a change in the effective refractive index and transmission properties of the immersion fluid. In an effort to address this problem, topcoat materials have been developed for use in forming a barrier layer between the immersion fluid and underlying photoresist layer. See, for example, U.S. Patent App. Pub. Nos. 2007/0212646A1 to Gallagher et al., and 2007/0087286 and 2010/0183976A1 to Wang et al.
In patterning high aspect ratio photoresist line-space patterns, the occurrence of resist pattern collapse has been observed. Pattern collapse is believed to take place during the resist development process due to the surface tension effects which can become magnified with decreasing spacing between high aspect ratio resist patterns.
There is a need in the art for topcoat compositions that address one or more problems associated with the state of the art, and for pattern-forming methods making use of such materials.